Hitherto, in magnetic recording madia having insufficient lubricating characteristics, the surface of the magnetic layer becomes smooth due to frictional contact with parts composing the deck for magnetic recording/reproduction to increase the friction coefficient of the magnetic layer. Such magnetic recording media comprising the magnetic layer having a high friction coefficient cause a cohesion phenomenon on the running contact parts due to the presence of fine water drops under, particularly, high humidity (relative humidity of 60% or more). When the cohesion phenomenon occurs in the magnetic recording medium and the running contact parts composing the deck for magnetic recording/reproduction, stick-slip phenomenon occurs resulting in generation of audible running noise, if running tension is superior to cohesive force. Further, recorded signals in the magnetic recording medium causing the stick-slip phenomenon produce frequency modulation in the running direction and, consequently, it becomes difficult to carry out reproduction of recording in a normal state. Further, in the magnetic recording medium used for recording, when the stick-slip phenomenon occurs during reproduction, reproduction in a normal state cannot be carried out and wow, flutter and jitter phenomena occur. Inversely, when the cohesion phenomenon occurs in magnetic recording medium and the running contact parts composing the deck for magnetic recording/reproduction, running stops and, consequently, it becomes impossible to carry out recording and reproduction, if cohesive force is superior to running tension. In this field of art, this phenomenon is called "tape squeal". Such magnetic recording media and decks for magnetic recording/reproduction have a very inferior commerce value.
The squeals originate from the materials of the running system for the magnetic recording media, running tension and running rate, etc. in the deck for magnetic recording/reproduction. Further, such squeals can originate from the smoothing of the surface of the magnetic layer and increases in the surface friction coefficient, etc. of the magnetic recording media.
In order to improve the surface lubricating characteristics of the magnetic recording media, many solid lubricants and liquid lubricants are used. Examples of such lubricants include conventional finely-divided inorganic and organic powders (Al.sub.2 O.sub.3, graphite, silica, Cr.sub.2 O.sub.3, ZnO and carbon black, etc.), organic surface active agents and lubricants (higher hydrocarbon compounds, aliphatic alcohols, aliphatic acids, aliphatic acid esters, aliphatic acid amides, aliphatic acid salts and aliphatic acid quaternary salts, etc.).
Carbon black has been frequently studied with respect to particle sizes for the purpose of improving the running property (for example, Japanese Patent Application (OPI) Nos. 62604/75 and 124123/81). It is known that when carbon black having a particle size of a certain value or more is blended, the face of the magnetic recording medium becomes coarse and the contact area of the magnetic recording medium during running decreases reducing the friction coefficient.
Although the running property can be improved to a certain degree by using such particles, it is still not sufficient.